Method of liming raw sugar juice



Jan. 1, 1957 c. L. PETERSON METHOD OF LIMING RAW SUGAR JUICE 2 Sheets-Sheet 1 Filed Aug. 17, 1951 INVENTOR.

0. Lynn Peterson ATTORNEY Jan. 1, 1957 c. PETERSON 2,776,229

METHOD OF LIMING RAW SUGAR JUICE Filed Aug. 17, 1951 2 Sheets-Sheet 2 000 ON RAW JUICE F l G.- 2

PURITY (TRUE) 0.0 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 oju o.| 2 0.13 0.|4

LIME SALTS AS 000 ON I00 BRIX INVENTOR.

F I G. 3 C Lynn Peterson ATTORNEY METHOD SF LIMING RAW SUGAR JUICE C. Lynn Peterson, Salt Lake City, Utah, assignor to Peterson Filters & Engineering Company, Salt Lake City, Utah, a corporation Application August 17, 1951, Serial No. 242,265

Claims. (Cl. 12748) My invention is directed to improvements in the refining of sugar.

Modern sugar refineries add substantial quantities of lime, usually in two stages, to raw sugar juice in order to precipitate the impurities naturally present. The quantity of lime employed varies considerably in the various plants, but is usually in excess of the exact quantity required for reaction with the impurities, carbonation being relied on for the removal of surplus lime. In instances where the juice is derived from sugar beets, approximately 40 lbs. of lime calculated as calcium oxide is added per ton of beets.

One of the principal objects of my invention is to provide a method and apparatus for substantially reducing the quantity of lime utilized in sugar purification, for eliminating treatment of the juice with carbon dioxide, and which permits highly accurate automatic control of reagent addition.

Other important objects of my invention include the provision of a process and apparatus for refining sugar which inherently insures the yield of a high purity sugar at reduced cost, which includes means for purification treatment, and which creates a substantially reduced quantity-of waste material, such as lime mud.

Other important objects of my invention will be disclosed in the following description of my invention and in the appended drawings, in which:

Fig. 1 is a schematic illustration of my refining process;

Fig. 2 is a graph indicating the change in pH value of various sugar juices occurring upon the addition of lime to the juice; and

Fig. 3 is a graphical representation of the effect of the addition of lime to sugar juice with respect to purity and the quantity of lime salts remaining in the juice.

Since the pH value of sugar juices extracted from sugar beets or sugar cane will vary according to the locality in which the beets or cane are grown, and in the same locality from year to year, it will be seen that considerable variation in pH value of the juice may be expected in any sugar plant. Attempts have been made to control the addition of lime to thesejuiccs of variable pH value with automatic proportioning equipment; but these in general have not been successful, due apparently to the inability of the apparatus to respond properly to variations in the character of the juice being treated.

I have found that as lime is added to sugar juice, the increase in pH value is not proportional to the quantity of lime added and it is believed that this characteristic is primarily responsible for the difliculties previously encountered in the use of automatic proportioning equipment. A major contribution of the present invention is embodied in the discovery that this difficulty can be overcome by standardizing the juice prior to the addition of lime with an alkali metal base, such as sodium hydroxide. This base is added to the juice in quantities sufficient to attain a juice having a standardized predetermined pH value, usually 8.0. The subsequent addition 'ice of lime to this standardized juice produces a uniform, immediate, and predictable change in the pH value of the juice, with the result that automatic proportioniug equipment responsive to variations in the pH value of the juice may be successfully employed and the quantity of lime added to the juice closely controlled by the automatic equipment.

i have further discovered that the addition of excess lime to such a standardized juice adversely affects the purity of the juice and that a higher order of purity can usually be obtained by substantially reducing the quantity of lime employed. In a majority of instances, the point of maximum purity and minimum residual lime salts is reached when the pH value of the juice is raised by the addition of lime from a pH value of about 8 to a value of between 9 and 11.5, a value of 10 being the usual approximate point of maximum purity. Increasing the pH value of the juice beyond this point by the addition of lime increases the quantity of lime salts remaining in the juice and reduces the purity to a substantial degree. Since close control of the pH value of the juice can be obtained automatically by utilization of my invention, I am able to obtain a sugar of exceptionally high purity, which requires in its processing less than one-tenth the amount of lime conventionally employed.

The character of the precipitate formed by the ad dition of lime as above described differs somewhat from the precipitate ordinarily obtained upon the addition of lime to a sugar juice and is quite difiicult to separate by filtration. This difliculty is overcome by the addition of substantial quantities of filter aid to the juice prior to filtration, but obviously if the desired over-all economy of processing is to be obtained, efiicient means for recovering and reconditioning the filter aid must be provided.

I have found that the diiference in density between the ordinary filter aids, such as diatomaceous earth, asbestos, bone charcoal, etc., and the precipitate formed in my process is suificient to permit separation of the filter aid and the precipitate by gravity or centrifugal force. If a diatomaceous earth or other similar silica compound is employed as a filter aid, separation can be accomplished by subjecting the material to froth flotation in the presence of a suitable collector reagent. If desired, after separation, the filter aid may be further treated, as by acids or calcination prior to recycling.

In Fig. 1, I have illustrated diagrammatically a typical sugar refining installation in which a conduit 10 dis charges raw juice to a screen or centrifuge 11 which separates pulp and fiber from the juice, the solids being discharged through a conduit 13. A pump 12 forces the juice into a heater tank 14, where the temperature of the juice is increased to the desired degree, preferably on the order of F. Juice is discharged from the heater 14 through a conduit 16 to a metering orifice 17, which discharges into a limer 18 through a conduit 19. Conventional pH control electrodes, indicated at 21, are placed in communication with conduit 19, the output from the electrodes being suitably amplified and connected in conventional manner to .a proportioning pump 22 having an inlet communicating with a caustic tank 23 and an outlet communicating with the orifice plate 17 through a conduit 24. The specific type of pH control equipment utilized does not constitute a part of my invention and substantially any of the commercially available devices may be employed.

The limer 13 is preferably a vacuum limer of the type disclosed in my Patent No. 2,520,957, issued September 9, 1950, and utilizes an impeller for quickly and thoroughly distributing lime into the juice under sub-atmospheric pressure. A jet pump 26 may be employed for maintaining the interior of the limer 18 under vacuum.

Milk of lime is discharged by a pump 27 into a separator 28, which removes sand and other impurities from the lime before discharge into a tank 29, the outlet of which is connected with the limer 18 through a proportioning pump 31.

Preferably, the limer 18 is disposed in an elevated position and includes a depending barometric leg 32, the end of which is disposed below the liquid level in a tank 33. Heating coils 34 and an impeller 36 are mounted in the tank 33, the latter being utilized not only to circulate the juice across the coils 34, but also to mix filter aid discharged into the tank 33 from a suitable hopper 37 into the juice. Another set of pH electrodes 38 are disposed in the tank 33 in contact with the juice, the output from these electrodes being suitably amplified and transmitted by a wire 39 to the proportion pump 31, which controls the quantity of lime added to the juice in the limer.

The treated juice containing the necessary quantity of filter aid is drawn from the tank 33 by a non-churning type of pump 41 and discharged via conduit 42 into a filter thickener 43, the latter preferably being of the type disclosed in my copending application, Serial No. 172,607, filed July 7, 1950. Clarified juice from the filter thickener 43 is discharged through a conduit 44 for further processing, the collected solids together with a portion of the remaining juice being forced by a pump 46 to a tank 47. Overflow from the filter thickener 43 is recycled through a conduit 48 to the tank 33.

Water is added to the slurry in the tank 47 from a water inlet 51, an agitator 49 being employed for repulping the solids and forming a slurry suitable for filtration. The resulting slurry is conveyed to a filter 52, the filtrate being conveyed by a conduit 53 to conduit 44. The solids discharged by the filter 52, consisting principally of filter aid and lime-bearing precipitates, are diluted with water from water inlet 51 and discharged into a filter aid separation device 54, where the filter aid is separated from the precipitate and the latter discharged through conduit 56.

As previously noted, the precipitate formed in my process is flocculant and siliceous. Although markedly reduced in volume by comparison with the quantity of precipitate ordinarily obtained, it is particularly dilficult to filter and requires the use of filter aid, the quantity preferably being at least double the weight of the precipitate to be treated. Several different filter aids have proven satisfactory for this purpose, as for example, diatomaceous earth, asbestos, and bone charcoal. All of these materials can be separated from the precipitate by allowing the filter aid to settle by gravity in a tank. The precipitate, being lighter than the filter aid, may be discharged from the upper level of the tank and the purified filter aid may be discharged from the lower level. In a similar manner a conventional centrifuge may be employed for separating the two materials.

If diatomaceous earth or other similar silica compound is employed as a filter aid, froth flotation may be utilized to effect a very satisfactory separation of the precipitate and filter aid. Conventional froth flotation equipment is employed in this process, together with a suitable collector reagent, such as Armac T. This reagent is a mixture having a mean molecular weight of 331 and a melting point of 65 0., consisting approximately of 30% hexadecyl primary amine, 25% octadecyl primary amine, and 45% octadecenyl primary amine reactor after formation with acetic acid to form a complex amine acetate. It will be understood, of course, that other suitable collector reagents for the flotation of silica compounds may be substituted. In the presence of such a collector reagent the diatomaceous earth filter aid is concentrated in the flock overflow of the flotation cell, the undesired precipitate being discharged as tailings from the process.

The filter aid is discharged from the separation device 54 into a tank 57, where it is repulped by an agitator 58 and discharged through a pump 59 to a filter 61. The

filtrate from the filter 61 may be discarded, while the filter aid, which forms the filter cake of the filter 61, may be discharged either directly into the tank 33 or into a filter aid treatment device 62, which in turn discharges into the filter aid feed hopper 37. In the device 62, the filter aid may be calcined to eliminate insofar as possible the last traces of impurities.

Sugar refineries will process sugar beets or sugar cane grown in a number of various localities, with the result that the pH value of the juice entering the process will vary considerably on a day to day basis. In Fig. 2, the curves A, B, and C indicate the response of juices of varying pH values to the addition of lime, it being noted that the change in pH value for each of these juices upon the addition of a given quantity of lime calculated as calcium oxide varies considerably and becomes relatively constant only after a pH value of approximately 11.5 has been attained. It will also be noted that the slope of the curves A, B, and C in Fig. 2 is relatively fiat indicating that considerable quantities of lime are required to produce an appreciable change in the pH value. These factors make it exceptionally ditficult under ordinary circumstances to control the addition of lime by automatic proportioning equipment based upon pH value of the juice under treatment.

Referring to curve E in Fig. 3, it will be noted that the purity of the sugar juice increases with the pH value up to a certain point in the neighborhood of a pH value of 10 and thereafter decreases. Similarly, the lime salts remaining in the juice decrease upon the addition of lime up to a certain pH value, as indicated by curves F and G, until an optimum point is reached and thereafter increased. Thus, it becomes clear that the addition of excess lime harmfully affects the purity of the juice and that optimum purity with minimum residual lime salts may be obtained when the quantity of lime added is sulficient only to increase the pH value of the juice to between 9 and 11.5, a pH value of 10 usually representing the approximate optimum value.

The erratic response of raw sugar juice to the addition of lime as indicated by curves A, B, and C in Fig. 2 can be avoided by first standardizing the juice by the addition of an alkali metal base such as sodium hydroxide or potassium hydroxide to a predetermined pH value above the normal pH value of the juice. In most instances, this predetermined pH value should be 8.0. This is, of course, accomplished by maintaining a supply of approximately 20% sodium hydroxide in the tank 23 and adding it to the juice at the orifice plate 17 through the proportioning pump 22. After standardization in this manner, the response of the juice to the addition of lime is indicated by the curve D in Fig. 2. The response under such circumstances will be constant and in addition the slope of the curve D is sufliciently sharp to permit accurate and satisfactory operation of the proportioning pump 22 under the control of the electrodes 21. It is therefore possible to not only radically reduce the quantity of lime added but also to automatically control the pH value in such manner that the optimum pH value is maintained regardless of fluctuations in the pH value of the raw juice.

Various types of limers 18 may be utilized, but I prefer to employ a vacuum limer of the type indicated, since utilization of this apparatus not only decreases the total quantity of lime required, but also insures that the slope of curve D between pH values of 8.0 and 11.0 will be sharp.

From the foregoing, it will be noted that the quantity of lime required for treatment of the juice is on the order of 0.06 to 0.15% calcium oxide, rather than the conventional 1.0 to 2.0% per ton of beets. The purity of the juice, however, is fully equivalent or superior to that obtained by utilization of the conventional liming-carbonation process. It is also to be noted that carbonation of the juice is unnecessary and that the quantity of precipitate formed is substantially less than that obtained from the conventional process. The latter consideration is believed to be of importance, since the disposal of such precipitates constitutes a serious problem at a majority of the sugar factories.

What is claimed is:

1. In the process of treating raw sugar juice so as to condition it for extraction of sugar content, the improvement which comprises standardizing such a raw juice by introducing an alkali metal hydroxide in an amount sufficient to raise the juice to an alkaline pH of about 8, passing the resulting juice directly to a liming stage, then introducing a liming composition to the standardized juice in amounts proportioned to the weight of the juice into which it is introduced until the pH of the juice is raised to a point within the range af about 9-115 at which maximum purity rise is obtained with a minimum of residual lime salts, and passing the juice so treated to a clarifying filtration stage for removal of substantially all precipitated insoluble content prior to delivering the clarified juice to the sugar extraction stage.

2. In the process of treating raw sugar juice so as to condition it for extraction of sugar content, the improvement which comprises standardizing such a raw sugar juice by introducing sodium hydroxide in an amount sufficient to raise the juice to an alkaline pH of about 8 which is the lowest pH at which a smooth reproduceable curve results from plotting pH against amount of lime added to the juice, passing the resulting standardized juice to a liming stage, then introducing milk of lime into the standardized juice in amounts proportioned to the weight of the juice into which it is introduced until the pH of the juice is raised to a point within the range of about 9l1.5 at which maximum purity rise is obtained with a minimum of residual lime salts, and passing the juice so treated to a clarifying filtration step for removal of substantially all precipitated insoluble content prior to delivery of the clarified juice to the sugar extraction stage.

3. In the process of treating raw sugar juice so as to condition it for extration of sugar content, the improvcment which comprises standardizing such a raw sugar juice by introducing sodium hydroxide in an amount sufficient to raise the juice to an alkaline pH of about 8 which is the lowest pH at which a smooth reproduceable curve results from plotting pH against amount lime added to the juice, passing the resulting standardized juice to a liming stage then introducing milk of lime into the standardized juice in amounts proportioned to the weight of the juice into which it is introduced until the pH of the juice is raised to 10.0 at which maximum purity rise is obtained with a minimum of residual lime salts, and passing the juice so treated to a clarifying filtration step for removal of substantially all precipitated insoluble content prior to delivery of the clarified juice to the sugar extraction stage.

4. In the art of purifying raw sugar juice wherein the raw juice is introduced into a limer and a liming composition is added to the juice at predetermined rates by operation of an automatic control responsive to the pH of the juice in the limer, the improved method of operation which comprises adding an alkali metal hydroxide to the raw juice before operation of the automatic liming control in a quantity suificient to increase the pH of the raw juice to a standardized value of about 8 such that upon addition of lime thereto, the curve representing pH versus quantity of lime added will have a major portion of a substantial slope over a relatively narrow range of slope and will throughout its extent from the initial pH to the maximum thereof be a smooth curve of progressing decrease in slope, and immediately thereafter initiating operation of the automatic control to etfect addition of lime into the resulting standardized juice until the pH of the juice reaches a predetermined value within the said major portion of the pH-lime curve.

5. In the art of purifying raw sugar juice wherein the raw juice is introduced into a limer and a liming composition is added to the juice at predetermined rates by operation of an automatic control responsive to the pH of the juice in the limer, the improved method of operation which comprises adding sodium hydroxide to the raw juice before operation of the automatic liming control in a quantity sufiicient to increase the pH of the raw juice to a standardized alkaline value of about 8 such that upon addition of lime thereto, the curve representing pH versus quantity of lime added will have a major portion of a substantial slope over a relatively narrow range of slope and will throughout its extent from the initial pH to the maximum thereof be a smooth curve of progressing decrease in slope, sampling and testing the standardized juice to determine the pH which an addition of lime to the standardized juice produces an optimum purity with a minimum of residual lime salts, and immediately thereafter initiating operation of the automatic control to efiect addition of lime to the resulting stand ardized juice in the limer to increase the pH thereof to the predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 805,081 Lewicki Nov. 21, 1905 1,404,185 Blomeley Jan. 24, 1922 1,526,520 Boeck Feb. 17, 1925 1,533,033 Sauer Apr. 7, 1925 1,956,741 Hornberger May 1, 1934 2,071,776 Teatini Feb. 23, 1937 2,216,754 Sanchez Oct. 8, 1940 2,284,122 Boyd May 26, 1942 2,391,843 Rawlings Dec. 25, 1945 2,520,957 Peterson Sept. 5, 1950 2,557,996 Peterson June 26, 1951 2,563,006 Collier Aug. 7, 1951 

1. IN THE PROCESS OF TREATING RAW SUGAR JUICE SO AS TO CONDITION IT FOR EXTRACTION OF SUGAR CONTENT, THE IMPROVEMENT WHICH COMPRISES STANDARDIZING SUCH A RAW JUICE BY INTRODUCING AN ALKALI METAL HYDROXIDE IN AN AMOUNT SUFFICIENT TO RAISE THE JUICE TO AN ALKALINE PH OF ABOUT 8, PASSING THE RESULTING JUICE DIRECTLY TO A LIMING STAGE, THEN INTRODUCING A LIMING COMPOSITION TO THE STANDARDIZED JUICE IN AMOUNTS PROPORTIONED TO THE WEIGHT OF THE JUICE INTO WHICH IT IS INTRODUCED UNTIL THE PH OF THE JUICE IS RAISED TO A POINT WITHIN THE RANGE OF ABOUT 9-11.5 AT WHICH MAXIMUM PURITY RISE IS OBTAINED WITH A MINIMUM OF RESIDUAL LIME SALTS, AND PASSING THE JUICE SO TREATED TO A CLARIFYING FILTRATION STAGE FOR REMOVAL OF SUBSTANTIALLY ALL PRECIPITATED INSOLUBLE CONTENT PRIOR TO DELIVERING THE ELARIFIED JUICE TO THE SUGAR EXTRACTION STAGE. 